In order to operate a terminal using a touch panel, a user faces a screen on which output of the terminal is displayed, and operates the terminal by operating a keyboard or a mouse, or by touching the screen with one or more fingers. In other words, the user needs to directly touch the touch panel for the input into the terminal using the touch panel, and it is difficult for the user to operate the terminal from a free position of a hand or a free posture. In view of this, a method has been developed for operating a portable terminal or peripheral equipment using the movement of an upper limb, while wearing on one's body or holding in a hand a device that measures acceleration or angular velocity.
As the technology described above, a device is known that detects an angle corresponding to a change in orientation of a directional vector of a hand and a forearm of a user from an image obtained by capturing a user's movement, and that determines whether a motion to turn pages has been made (for example, Japanese Laid-open Patent Publication No. 2012-242901). In this technology, a user does not need to learn operations of a device for input, and can cause the device to perform corresponding control by merely making an ordinary motion to turn pages.
In addition, a technology is known for capturing an image of a position of a user's hand, expressing the position by a relative distance and a relative angle from a specified point, such as a center position of the user's chest, and associating the relative position and the relative angle with a position of a cursor of an input device (for example, Japanese National Publication of International Patent Application No. 2010-534895). This technology enables easy selection of an item from a group of items, such as the selection of a letter from a group of alphabetic letters, or the selection of a function from a plurality of functions.
In addition, a technology is known in which a user executes a game while holding a controller that is an operation device of a game machine, and re-specifies a reference posture of the controller by pressing a button of the controller (for example, International Publication Pamphlet No. 2011/122214). In this technology, the controller includes an angular velocity sensor, and outputs, to the game machine, a detection signal of an angular velocity detected by the angular velocity sensor. The detection signal of the angular velocity sensor is a signal that is obtained by detecting an angular velocity at which the controller is rotated around each of the coordinate axes of a three-dimensional orthogonal coordinate system that is generated in the controller. The game machine detects, from the detection signal, rotation angles from a reference posture of the controller, and performs control in accordance with a change in the rotation angle. This technology prevents, for example, a situation in which errors due to adrift of the angular velocity sensor are accumulated in an integrated value of angular velocities, the detected rotation angles become inaccurate over time, and it becomes impossible to appropriately control the movement of characters or objects that are displayed on a display of the game machine.
However, in a technology for detecting a position or a posture of an extremity of a body part that starts a motion, such as a hand, a toe, or a head, so as to perform input, a user's sense of direction deviates from corresponding operations. Therefore, there is a problem wherein the user feels unconformable and is likely to require a significant effort to learn operations. In addition, in a method for calculating a posture angle from an acceleration during a motion, there is a problem wherein an error due to noise is likely to occur.